A new class of soft contact lenses, water gradient silicone hydrogel contact lenses, have been developed and successfully introduced in the market. This new class of silicone hydrogel contact lenses is characterized by having a water-gradient structural configuration, an increase from 33% to over 80% water content from core to surface. This unique design delivers a highly-lubricious and extremely-soft lens surface. Such soft contact lenses can be produced according to a cost-effective approach that is described in U.S. Pat. No. 8,529,057 (herein incorporated by reference in its entirety) and involves a step of crosslinking and covalently attaching of a water-soluble highly-branched hydrophilic polymeric material onto lens surfaces to form surface gels.
According to U.S. Pat. No. 8,529,057, a water-soluble highly-branched hydrophilic polymeric material is prepared by partially reacting a polyamidoamine-epichlorohydrin (PAE) with a wetting agent, at various concentration ratio of PAE to the wetting agent and at a reaction temperature for a given reaction time, to achieve a desired lubricity of the surface gels while minimizing or eliminating surface defects (e.g., surface cracking, etc.). Although this new approach can provide hydrogel contact lenses having a water-gradient structural configuration, its applicability and advantages can be limited by the limited availability of hydrophilic copolymers having a versatility and controllability in the levels of reactivity and/or contents of reactive functional group towards the azetidinium groups of PAE.
Therefore, there is still a need for reactive hydrophilic polymers having desired level of reactivity and/or contents of reactive functional groups for producing water-soluble highly-branched hydrophilic polymeric material useful for producing water gradient contact lenses.